The present invention relates to a molten metal plating apparatus of the type in which the run-out of the molten metal contained in a horizontal molten metal plating tank inserted in a horizontal strip pass line is prevented or controlled to a desired value at the feeding and discharging ends of the plating tank for the strip.
Continuous molten metal plating methods and apparatus for the coating of steel strip with zinc, tin, lead and aluminium and their alloys are known in the art in which the coating of the strip to be plated is effected by obliquely introducing the strip from the top of the plating tank into the plating bath and vertically delivering the strip to the top of the plating tank again after passing through around the lower side of sink rolls arranged at the bottom of the plating bath in the tank.
A disadvantage of the method and apparatus of the above type is that since the sink rolls are arranged at the bottom of the bath in the plating tank to change the direction of movement of the strip, the sink rolls are eroded due to their contact with the molten metal (plating bath) and the strip, and this erosion eventually reaches to such an extent that surface defects are caused in the coated strip, thus necessitating the periodic replacement of the sink rolls. Another disadvantage is that the coating of heavy-gauge steel strip or plate requires the use of sink rolls having a greater diameter, and at present the maximum strip thickness for successful coating is considered to be on the order of 4 to 5 mm, thus failing to meet the requirements for the recent continuous molten metal plating of heavy-gauge steel strip or plate. Still another disadvantage of the method and apparatus of the above type is that due to the fact that the strip emerges vertically from the plating bath, a portion of the metal deposited on the strip runs down due to the force of gravity, and therefore in order to ensure an increased coating weight and uniform plating of the strip there is a certain limit to the maximum coating weight which is, for example, 300 g/m.sup.2 in the case of zinc plating, in consideration of the viscosity of molten metal, the surface properties of base metal, etc. And therefore such conventional method and apparatus are not capable of providing coating thicker than the limit just stated.